Radio receiving system



Feb. 7, 1933. v. c. MACNABB 1,896,825

7 RADIO RECEIVING SYSTEM Filed Nov. 1931 30.13.17.190 047/7014! J9 VJ 70/1 Patented-Feb. 7, 1933 PATENT OFFICE VERNON C. MACNABB, OI PHILADELPHIA, PENNSYLVANIA, ASSIGNOR ATWATEB KENT MANUFACTURING COMPANY, OF PHILADELPHIA,

1 PORATION OF PENNSYLVANIA RADIO RECEIVING SYSTEM Application filed November 5, 1931. Serial No. 573, 100.

My invention relates to radio receiving systems in which oscillations locally produced interact with the received signal-representing oscillations to effect beats, for heterodyne or superheterodyne reception; and more particularly my. invention relates to the method of and apparatus for locally generating oscillations for interaction with signal-representing oscillations as aforesaid, or with other oscillations.

In accordance with my invention the system for locally generating oscillations comprises a vacuum tubehaving regeneratively coupled output and input circuits or systems, with pI'OVlSlOIl of means for procuring a substantially constant voltage character-,

istic, and for at the same time insuring that the adjustable element of a variable frequency-determining reactance, specifically a condenser, of the generator of oscillations may be mechanically coupled to or adjusted in unison with the adjustable element of a reactance, specifically a condenser, utilized in tuning to some other frequency or the signal frequency, to maintain a constant beat frequency.

More particularly, either the output or input circuit or system, coupled both inductively and capacitatively, comprises inductance and a plurality of serially connected capacities, at least one of which is variable for varying the frequency of the generated oscillations, another of which'i-s common to the output and input circuits, and alone or in serieswith a third capacity bears such relation to the variable capacity that its adjustable' element may be coupled toor adjusted in'unison with the rotatable element of a variable capacity utilized in turning to the frequency of the signal-representing or other oscillations with which the locally generated oscillations shall react.

My invention resides in a system of the character hereinafter described and claimed. For an understanding of my invention and for an illustration of one of the various forms it may take, reference is to be had to the accompanying drawing, in which:

Fig. 1 is a diagrammatic illustration of a terminal of the loop superheterodyne receivingsystem embodying my invention;

Fig. 2 is a groupof curves illustrating characteristics of the oscillation generating system;

Fig. 3 illustrates a modification.

For brevity that form of my invention is illustrated and described in detail in which the significant variable reactance, specifically a condenser, of the oscillation generator, and its associated rcactances, specifically condensers, are disposed in the input system of the oscillation generator; it shall however be PENNSYLVANIA, A C03 1 understood they may be disposed in the output system in like arrangement for the'same purposes and results, with the input and output systems magnetically and capacitatively coupled as before.

Referring to Fig. 1, V represents a thermionic vacuum tube of any suitable type comprising the anode or plate a, control grid 9, and cathode la, or, when desired, comprising inaddition a fourth electrode a, a shield or screen grid. In this example, the tube V is a detector, more particularly the first detector of a superheterodyne receiving system comprising, beyond the tube V', the intermediate or beat frequency amplifier system I, the second detector stage or s stem D2, audiofrequency amplifier system and the signaltranslating instrument G indicated, by way of example, as an electrodynamic loud speaker.

In the amplifier system I a constant beat or intermediate frequency iswzmplified in one or more stages, comprising preferably one or more circuits tuned to that frequency. On the input side of the detector V are provided the antenna or equivalent absorption structure between which and earth or counter capacity E is the primary P of a radio frequency transformer to which is couplcd the secondary S which with the primary Pl constitutes the inductance of a 100 circuit tunable by the variable condenser one may be connected to earth, as indicated. Oou led tcthe primary P1 is the secondary S1, 0 a second radio frequency transformer, in shunt withwhich is connected the variable condenser K1. S1

' which is connected to the control grid 9. The grid is biased to a suitable negative value and K1 constitute a tunable loop, one terminal of which is grounded and the other of 5 by means of a self bias or resistance R2 cated by the member 1, for uni-control.

Between the cathode is and one terminal of the loop S1, K1, or elsewhere on the input or output side of detector V, is interposed an inductance or coil L2 coupled to the inductance L of the generator of local oscillations, whereby upon the input system of the tube V there are impressed locally generated oscillation voltages at frequencies which so vary that the diflerence between them and the frequencies of the signal-representing oscillations shall be fixed and constant, with the efiect that the beater intermediate frequency is constant A current component of beat frequency appears in the plate circuit of the tube V and is passed on to the interv mediate frequency amplifier I aforesaid. By

preference the frequency of the locally generated oscillations is throughout the range higher, by say 130 kilocycles, than the frequency of the signal-representing oscillations.

By way of example, when the circuits tuned by the condensers K and K1 are used in broadcast reception, the frequency of the oscillations representing the signals may vary in frequency from 550 to 1500 kilocycles, in which case the oscillator frequency will vary from 680 to 1630 kilocycles, affording a constantv beat or intermediate frequency of 130 kilocycles.

It is desirable that the voltage of the locally generated oscillations as appearing I frequency of the locally generated oscillations, shall partake. of adjustments equal to, or having constant relation to, the extents of adjustments of the rotor or rotors of the preselector condensers K and K1, while constant frequency difference is maintained. At 2 is indicated for this purpose a member mechanically uniting or coupling the rotors or adjustable elements of the tuning condenser K1 and the variable or tuning condenser C of the oscillation generator.

,The local generator of oscillations "comprises the vacuum tube V1 having the anode tube V1 (or in its plate circuit or output sys-.

tem as hereinafter stated) is provided the inductance L which is preferably made suitably smaller thanthe inductances of the preselector circuits tuned by the condensers K and K1. In series with thej'aforesaid va: riable condenserC are the condensers C1 and C3, preferably of fixed magnitudes; these three condensers are all in series with each other and in shunt with the inductance L forming a resonance loop, one terminal of which is connected to the grid 9, while the, cathode is is connected to earth E and to a;

point between the condensers C and C1, whereby the voltage im ressed upon the grid 9' is dependent upon the magnitude of the capacity of the condenser G, in shunt with which may be used a small fixed trimming or calibrating condenser C2. From the terminal of the inductance L remote from the grid 9 there is a connection to earth or groun E through the resistance R1.

From the anode or plate a of the tube V1,

when inductance L is in the plate circuit or output system.

V1 is magnetically couple by the inductance L1,'a'nd capacitatively by the condenser C1,

The output circuit or s stem of the tube to the grid or input system or circuit of the tube, causin by regenerative action the production of ocal oscillations, to be utilized as aforesaid in heterodyne rece tion or for any other purpose, and whose requency is largely determined by inductance L and capacities C, C1 and C3.

Referring to Fig. 2, in which ordinates are voltages across the terminals of the second ary or inductance L2, or the voltages applied to the system including the detector V, and abscissae are frequencies in kiloeycles, the curve A is the characteristic of an oscillator in which the output system or plate circuit is coupled to the input system or grid circuit inductively as indicated generically by the inductive coupling L, L1, Fig. 1. The voltage rises or increases, rapidly with increase in frequency.

The curve B, showingrapid decrease or fall of voltage with increase in frequency, is the characteristic of an oscillator in which the output system or plate circuit is coupled to the grid circuit or input system capacitatively, as indicated generically in Fig. 1 as effected by the condenser C1.

When, however, the output system or plate circuit is coupled both capacitatively and magnetically to the input system or grid circuit, as illustrated by Fig. l, and when the constants of the circuits are suitably chosen as to magnitudes, there results the characteristic curve 0, Fig. 2, for which the voltage applied to the detector system is substantially constant throughout the range of frequencies of the locally generated oscillations.

Accordingly one of the desiderata of myinvention is accomplished by both magnetically and capacitatively coupling the output to the input circuit of the oscillator, but there remains a further desideratum, to wit, that the rotor or adjustable element of the variable reactance, specifically condenser C of the oscillator may be adjusted in unison with, as through a mechanical coupling, the

rotor or adjustable element or elements or one or more of the tuning reactances, specifically condensers as K, K1, of the system tunable to the various frequencies of the received signal-representing or other oscillations, while maintaining constant difference between the signal-representing and locally generated oscillations.

This latter condition is attained by suitable relation to the maximumcapacity 9f the tuning condenser C of the remainder of the capacity in series therewith in the tunable loop and inductance L of suitable magnitude. This is attained by providing capacities C1 and C3 of such magnitudes that their capacity as a series combination is suitably large with respect to the maximum capacity to which the condenser C is adjusted. That is to say, the product of the capacities C1 and 03 divided by their sum is large with respect to the maximum capacity of the variable condenser C. Under these circumstances, the rotor or adjustable element of the condenser C may be adjusted in unison with or mechanically coupled with the adjustable element or elements of the condensers K and K1, with the effect that the frequency of the locally generated oscillations will, throughout the range of adjust ment or tuning, differ from the frequency of the signal-representing oscillations to intermediate frequency.

It is at the same time further desirable while simultaneously those input and output systems are magnetically coupled, so that the voltage impressed upon the detector system through the coupling L, L2 shall be constant throughout the frequency range of the locally generated oscillations.

While the capacity in series with that of the tuning condenser C may be a composite of two or more capacities C1 and C3 as illus trated, it shall be understood that a single capacity as Cl may be employed, large with respect to the maximum capacity of the tuning condenser C, serving at the same time as capacity coupling of the input and output systems of the tube V1, with omission of the condenser C3, or utilization of another condenser, outside of the tunable input loop, in such position as to serve as a stopping condBenser with respect to the plate circuit source From the foregoing it will be apparent that the condenser 01 serves either alone, or in association with the condenser C3, as a capacity making possible the uni-control aforesaid, and at the same time condenser Cl serves as the capacity of a capacitative and inductive coupling between the output and input systems of the tube V1 for regenerative production of oscillations with the aforesaid constant voltage characteristic.

For the purposes hereinbefore described, for the broadcast range of frequencies aforesaid, and for procuring locally generated oscillations of frequencies ranging from 680 to 1630 kilocycles, the various elements may have magnitudes as follows:

Each of the tuning condensers K and K1, a capacity variable from 50 to 400 micromicrofarads.

Each of the inductances associated with the condensers K and K1, 200 microhenries.

Of the local oscillator,

(1+ C2=50 to 400 micro-microfarads.

C1 5,000 micro-microfarads.

C3=2,040 micro-microfarads.

L=177 .5 microhenries.

L1=744 microhenries.

Mutual inductance of L and L1=23.3 microhenries.

R=20,000 ohms. As hereinbefore indicated, it is not essential that the group of elements such as the inductance L and its associated capacities C,

' C2, C1 and C3 be disposed in the input system of the oscillator tube. It shall be understood that they, or any essential part of them, may be in the output system or plate circuit of the oscillator tube V1, the condenser C1 being as before common to the output and input systems to capacitatively couple, them, and the inductance L1 may be in the input" or grid circuit and coupled to the inductance L when in the output system for magnetically coupling the output and input systems or circuits. The locally generated oscillations are in either the input or output system of tube V1, upon the system including the circuit tunable by the condenser or condensers K and K1. r

The foregoing is illustrated by Fig. 3 in which the inductance L and its associated condensers C, C1 and C3 are disposed in the anode or plate circuit of the oscillator tube V1, with a connection to cathode or ground at E between condensers C and C1, and a connection to the grid from a point between the condensers C and C3 through the inductance L1 coupled to inductance L. The inductance L2, coupled to L, is disposed in the circuit upon which the generated oscillations are to be impressed, more specifically, as indicated in Fig. 1, upon a detector input circuit.

In series with the grid 9 of the tube V1 is a condenser K3 having a capacity of the order of 250 micro-microfarads; there is provided also between grid and cathode resistance R3 which may be of the order of 100,000 ohms.

lVhen the several reactances are disposed in the output system as illustrated by Fig. 3, there are again obtained the two functions or objects of my invention described in connec tionwith Fig. 1, to wit, first, the constanc of voltage impressed upon the system inclu ing one or more of the tuning condensers K or K1 throughout the range of frequency of the locally 'enerated oscillations; and, second, the tracking of the variable condenser C, now in the output system of the oscillator tube, with the variable condenser or con- 'densers such as K and K1 of the system upon which the locally generated oscillations are impressed; that is to say, the variable con 'densers again may be adjusted in unison, as through a mechanical coupling 2, throughout the frequency range while maintaining a constant difference between the frequencies of the locally generated oscillations and the oscillations in the system upon which the locally generated oscillations are impressed.

What I claim is:

1. In radio reception, the method which comprises tuning in a receiving system to signal-representing oscillations throughout a range of frequencies thereof by varying a capacity, locally generating oscillations by coupling the output system of a thermionic tube to its input system magnetically and capacitatively through a capacity common to said output and said input systems, through an inductive coupling impressing upon said receiving system locally enerated oscillations, by said magnetic an capacitative couplings rendering constant throughout the frequency range the voltage of the oscillations so impressed on said receiving system, controlling the frequency of the generated oscillations by varying another capacity in said input system, and utilizing said capacity common to said output and input systems to modify the action of said last named variable capacity in series therewith in said input system to cause the variable capacities of said receiving system and said input system to be adjustable in unison to efi'ect throughout the,

frequency range a constant difference between the frequencies of the locally generated and signal-representing oscillations.

2. The combination with a system traversed by oscillations, said system comprising a circuit including inductance and a variable capacity for tuning to said oscillations throughout a range of frequencies thereof, a generator of oscillations, means for impressing upon said system oscillations produced by said generator, said generator comprising a thermionic tube having input and output systems, means for magnetically coupling said input and output systems of said tube, a capacity for coupling said input and output systems of said tube, said magnetic and capacitative couplings between said output and input systems being so related that the voltage of the oscillations'impressed upon said first named system b said means remains constant throughout t e frequency range of the locally generated oscillations, one of said systems of said tube comprising an inductance and said coupling capacity in series with acapacity variable to determine the frequency of the generated oscillations, said coupling and last named variable capacity being so related that said variable capacities of said first named system and of one of said tube systems shall be adjustable in unison to effect throughout the frequency range a constant difierence between the frequencies of the oscillations in said first named system and the locally generated oscillations.

3. A heterodyne receiving system comprising a circuit including inductance and variable capacity for tuning it to signalrepresenting oscillations throughout a range of frequencies thereof, a generator of oscillations comprising athermionic tube, means for magnetically coupling the output to the input system of said tube, a capacitative coupling between said output and said input systems comprising a capacity common to them, an inductive coupling for impressing locally generated oscillations upon said receiving system, said magnetic and capacitative couplings between said output and said input systems rendering constant throughout their frequency range the voltage of the oscillations impressed'on said receiving system, said capacity common to said output and input systems disposed in series with a variable frequency determining capacity in one of said systems of said tube to cause said range a constant difierence between the frequencies of the locally generated and signalrepresenting oscillations.

4. A heterodyne receiving system comprising a circuit including inductance and variable capacity for tuning it to signal-representing oscillations throughout a range of frequencies thereof, a generator of oscilla tions comprising a thermionic tube, means for magnetically coupling the output to the input system of said tube, a. capacitative couphng between said output and said input systems comprising a capacity common to them, an inductive coupling for impressing locally generated oscillations upon said receiving system, said magnetic and ca acitative couplings between said output an input systems rendering constant throughout their frequency range the voltage of the oscillations impressed on said receiving system, means for mechanically coupling the adjustable elements of said variable capacities of said circuit and said input system, and means for insuringconstant difi'erence between the frequencies of the locally generated and signalrepresenting oscillations during adjustment in unison of said adjustable elements comprising said capacity common to said output and input systems disposed in series in said input system with said variable capacity 7 thereof.

5. A heterodyne receiving system comprising a circuit including inductance and variable capacity for tuning it to signal-representing oscillations throughout avrange of frequencies thereof, a generator of oscillations, an inductive coupling for impressing locally generated oscillations upon said receiving system, said enerator comprising a thermionic tube having output and input systems, said input system including an inductance, a variable capacity and a pluralit of additional capacities all in series with eac other in circuit with said second named inments of said variable capacities of said cir-' cuit and said input system may be adjusted in unison throughout the frequency range while maintaining constant the difference between the frequencies of said locally generated and signal-representing oscillations,

said magnetic and capacitative couplings" between said output and input systems rendering constant throu hout their frequency range the voltage 0 the oscillations impressed upon said receiving system.

6. The combination with a system traversed by oscillations, said system comprising a circuit including inductance and variable capacity for tuning to said oscillations throughout a range of frequencies thereof,

a generator of oscillations, means for impressing upon said system oscillations produced by said generator, said generator com. prising a thermionic tube having output and input systems, said input system including an inductance, a variable capacity and another capacity in series therewith in circuit with said lastnamed inductance, connections to thcinput electrodes of said tube from the terminals of one of said lastnamed capacities. a third inductance coupled to said second named inductance, a connection from an anode to a cathode of said tube through said third inductance a'ud said other of said capacities, whereby the output and input systems of said tubes are magnetically and capacitatively coupled, and means mechanically coupling the adjustable elements of the variable capacities of said circuit and said input system for adjusting them in unison.

7: The combination with a system traversed by oscillations, said system comprising a circuit including inductance and variable capacity for tuning to said. oscillations throughout a range of frequencies thereof, a generator of oscillations, means for impressing upon said system oscillations produced by said generator, said generator comprising a thermionic tube having. output and input systems, said in ut system includplurality of additional capacities all in series with each other in circuit with said second named inductance, connections from the terminals of part of the capacity of said input system to the input electrodes of said tube, and means for magnetically and capacitatively coupling the output to theinput systems of said tube comprising a connection from an anode to a cathode of said tube through a point between two of said plu rality of capacities of said input system, and a third inductance in said connection coupled to said second named inductance.

8. The combination with a system traversed by oscillations, said system comprising a circuit including inductance and variable capacity for tuning to said oscillations throughout a range of frequencies thereof, a generator of oscillations, means for impressing upon said system oscillations produced by said generator, said generator com rising a thermionic tube having output an input systems, said input system including an inductance, a variable capacity and a plu- 105 ing an inductance, avaria le capacity and a Y rality of additional capacities allin series with each other in circuit with said second named inductance, connections from the terminals of a part of the capacity of said input system to the in ut electrodes of said tube, means for capacitatively coupling the output to the inputsystems of said tube comprising a connection from an anode to a cathode of said tube through a point between two of said plurality of capacities and through one of them, a third inductance in said connection coupled to said second named inductance for magneticallycoupling said input and output systems, and means for mechanically coupling the adjustable elements of the variable capacities of said circuit and said input system. I

9. The combination with a system traversed by oscillations, said system comprising a'circuit including inductance and variable capacity for tuning to said oscillations throughout a range of frequencies thereof, a generator of oscillations, means for impressing upon said system oscillations produced by said generator, said generator comprising a thermionic tube having output and input systems, said in ut system including an inductance, a varia le capacity and another capacity in series with each other in circuit with said inductance, a connection from a terminal of said variable capacity and said inductance to a control grid of said tube, a connection from a cathode of said tube to a point between-said serially connected capacities of said in ut system, a third inductance coupled to said second named inductance, and a connection from an anode of said tube to said cathode through said third inductance and a pointbetween said serially connected capacities of said input system.

10. The combination with a system traversed by oscillations, said system comprising a circuit including inductance and variable capacity for tuning to said oscillations throughout a range of frequencies thereof, a generator of oscillations, means for impressing upon said system oscillations produced by said generator, said enerator comprising a thermionic tube having output and input systems, said input system including an inductance, a variable capacity and another capacity in series with each other in circuit with said second named inductance, a connection from a terminal of said variable caersed by oscillations, said system comprising pacit and said inductance to a control grid a circuit including inductance and variable capacity for tuning to said oscillations throughout arrange of frequencies thereof, a generator of oscillations, means for impressing upon said system oscillations'produced by said generator, said generator comprising a thermionic tube hav ng output and input systems, said in at system including an inductance, a variable capacity and a plurality of capacities in series therewith and with each other in circuit with saidsecond named inductance connections from the terminals of a art of the capacity of said input system to t e input electrodes of said tube, a connection from one terminal-of said second named inductance to one of said input electrodes, a resistance connected between the other'terminal of said second named inductance and a cathode of said tube, a third inductance coupled to said second named inductance, and a connection from an anode of said tube to a cathode thereof through said third inductance to' a point between a pair] of said capacities of said input system.

12. The combination with a system traversed by oscillations, said system comprising a circuit including nductance and variable capacity for tuning to said OSCllltltlOIlS throughout a range of frequenciesthereof, a generator of oscillations, means for 1m pressing upon said system oscillations produced by said generator, said enerator comprising a thermionic tube having output and input systems, said input system including an inductance, a variab e capacity and a plu- 100 rality of capacities in series therewith and with each other in circuit with said second named inductance, connections from the terminals of a part of the capacity of said input system to input electrodes of said tube, v

a connection from one terminal of said second'named inductance to one of said input electrodes, a resistance connected between the other terminal of said second named inductance and a cathode of said tube, a third inductance coupled to said second named inductance, a connection from an anode of said .tube to a cathode thereof through said third con enser, characterized by the fact that the inpit and output systems of the oscillator tu are inductively and capacitatively coupled, the coupling capacity having such mag- 1 nitude that the voltage of the locally generated oscillations as impressed upon the signal receiving system is substantially constant throughout the range of frequency ad ustment of the oscillator, and that throng out the range of adjustment of said similar condensers in unison, the beat frequency between signal oscillations and locally produced oscillations is constant.

14. In a heterodyne receiver, a system traversed by signal oscillations comprising at least one circuit tunable by a variable condenser through a range of signal frequencies, a local oscillator system including a con denser adjustable through substantially the same range of capacity as said first condenser, means for coupling said oscillator system to said first system having the characteristic that the yoltage of the locally generated oscillations as impressed upon said first system increases with increase of frequency, and a'fixed condenser for coupling the input and output circuits of the oscillator tube of such magnitude that the voltage of the locally generated oscillations decreases with decrease of frequency compen citing for the rising characteristic of said ciupling means, and that through the range of adjustment of said similar condensers in unison, the beat frequency between si nal oscillations and locally produced oscillations is constant.

15. In a heterodyne receiving system comprising a system traversed by slgnal oscillat-ions inductively coupled to a local oscillater, the oscillator and said system having tuning condensers adjustable in unison through the same range of capacity, the method which comprises introducing into the coupling between the input and output circuits of the oscillator a capacitative impedance of such magnitude that the voltage of the locally produced oscillations as impressed uponsaid system is independent of their frequency, and that throughout the range of adjustment of said similar condensers, the beat frequency between the signal oscillations and the locally produced oscillations is constant.

VERNON G. MACNABB. 

